1. Field of the Invention
The present invention relates to an ink composition for ink jet recording and an ink jet recording process. In other words, the present invention relates to an ink composition for an ink jet printer which jets an ink droplet through an ink jet recording head to form an ink image on a recording medium such as recording paper and cotton or silk fiber. More particularly, the present invention relates to an ink composition for color ink jet printer and an ink jet recording process using said ink composition.
2. Description of the Related Art
An ink composition for ink jet recording normally must meet the following requirements:
(1) It must be little susceptible to irregular bleeding on a recording medium; and PA1 (2) It must undergo no change in physical properties and jettability and show no precipitation of solid matter.
In particular, the elimination of bleeding is important in the printing of color image. In color printing, a plurality of color ink compositions are printed on the same recording medium. In order to obtain a color print free of unevenly color area, it is necessary that the color border in the image be definite. To this end, the mixing of ink compositions in this area must be prevented.
In order to realize printing free of bleeding, various proposals have been heretofore made. For example, JP-A-58-188684 (The term "JP-A" as used herein means an "unexamined published Japanese patent application") and JP-A-62-288042 disclose a method which comprises printing while heating a recording medium. However, these patents don't disclose the use of an ink composition containing a thermoplastic resin.
In recent years, a pigment-based ink composition has been researched and developed for the purpose of realizing print free of bleeding as well as enhancing light resistance and weather resistance of image. For example, JP-A-6-116522 discloses an ink composition comprising a base composed of a water-soluble resin, a water-soluble solvent, a pigment and water having a specific additive incorporated therein. However, the ink composition disclosed in the foregoing patent is disadvantageous in that it causes clogging in the ink jet head. Thus, this ink composition cannot be applied to a recording system which comprises fixing simultaneously with the arrival of an ink composition to a heated recording medium. Further, JP-B-62-1426 (The term "JP-B" as used herein means an "examined Japanese patent publication"), JP-A-2-255875 and JP-A-4-18462 report an ink which comprises as ingredients water, a pigment and a resin emulsion to solve the problems of water resistance and light resistance as well as eliminate ink bleeding, which has been a problem with conventional dye-based inks.
When an ink composition comprising a thermoplastic resin is subjected to ink jet recording so that it is attached to a recording medium which is then heated to a temperature of not lower than a specific value, print bleeding can be well inhibited. It goes without saying that an ink composition for use in this recording process preferably undergoes no change in physical properties and jettability and shows no precipitation of solid matter during storage. Further, since this recording method requires the use of heat, the ink composition can be dried and solidified on the nozzle plate.
Further, if the ink composition used is a pigment-based ink composition having a great solid content, there arise the following two major problems attributable to this cause.
The first problem is that the ink composition may solidify in an ink passage from a normally sealed ink tank to an ink jet head due to some accident, possibly causing clogging in the recording head.
The second problem is that if the ink composition is attached to and dried on the plate having recording head nozzles arranged thereon and it cannot be rapidly removed by the cleaning operation of the recording apparatus, it may cause malinjection (deflected fly) of the ink composition during printing.